The role of amino acids in facilitating lead accumulation in microalgae: A quantitative analysis of functional group effects

In aquatic ecosystems, dissolved organic matter (DOM) enhances the adsorption of heavy metals onto microalgae by participating in the formation of algae–heavy metal–DOM ternary complexes, thereby increasing environmental risks. The functional groups in the DOM play a crucial role. However, a quantitative description based on these groups is lacking. This study investigates the effects of amino acids (AAs) with varying functional group ratios on the accumulation of lead (Pb) in Chlorella pyrenoidosa (C. pyrenoidosa) using batch experiments. Isotherm model fitting, and Fourier transform infrared spectroscopy (FTIR) are employed for characterisation. Results indicate that the addition of AAs facilitated Pb enrichment in microalgae. In particular, incorporating lysine (Lys) led to maximum accumulation, reaching 1.45 mmol g−1. The adsorption rate decreased after AA addition, particularly with Lys, dropping form 0.0032 g mg−1 min−1 to 0.0009 g mg−1 min−1. The reaction sequence showed carboxyl groups taking precedence over amino groups. The model developed from the data on Pb adsorption by C. pyrenoidosa following AA addition, demonstrated reliability with an R2 of 0.91 and an F-value of 157.6. Notably this study employed two-dimensional correlation spectroscopy (2D–COS), offering novel insights into the key roles of functional groups and their distinct contributions. These valuable insights contribute to intensive research on the ternary complex of algae − heavy metal − DOM and elucidating their ecological risks.